Conventionally, a technology disclosed in “Space-Time Block Codes from Orthogonal Design” IEEE Transactions on Information Theory, pp. 1456-1467, vol. 45, no. 5, July 1999 is known as a transmission method using a plurality of antennas. Hereinafter, the contents disclosed in this document will be explained using drawings.
FIG. 1 illustrates a conventional frame configuration. In this figure, transmission signal A and transmission signal B are signals transmitted from different antennas simultaneously. Transmission signal A and transmission signal B are consist of a symbol group containing the same data. SyA and SyB in the figure denote symbols and “*” denotes a complex conjugate. Transmission signal A is configured to form a frame of data symbols in an order of SyA, to −SyB* and the transmission signal B is configured to form a frame of data symbols in an order of SyB to SyA*. The transmission signal A and transmission signal B are synchronized with each other and transmitted. For this reason, data symbols SyA and SyB are transmitted simultaneously and data symbols −SyB* and SyA* are transmitted simultaneously.
FIG. 2 illustrates a conventional communication system. Transmission apparatus 11 is provided with antenna 12 and antenna 13 and transmits, for example, transmission signal A shown in FIG. 1 from antenna 12 and, transmission signal B from antenna 13 to reception apparatus 21. Reception apparatus 21 receives the signals transmitted from the antennas of transmission apparatus 11 by antenna 22. The signal received by antenna 22 is a combination of transmission signal A and transmission signal B, and therefore the received signal is separated into transmission signal A and transmission signal B and then demodulated.
In such a conventional communication system, transmission apparatus 11 transmits transmission signal A from antenna 12 and transmission signal B from antenna 13 and the signals transmitted from the antennas are received by the reception apparatus via different channel fluctuations (h1(t) and h2(t)). A conventional communication system takes advantage of this and adopts frame configuration shown in FIG. 1, and therefore, it is possible to improve reception quality of reception apparatus 21.
However, in the above described conventional communication system, SyA* and −SyB* are demodulated as SyA, SyB at the reception apparatus, and information of SyA* and −SyB* are substantially the same with SyA, SyB. This means that the same information is transmitted twice, resulting in low data transmission efficiency.